In a normal heart, regular waves of electric depolarization of the cellular membrane propagate to trigger the mechanical contractions. Life-threatening arrhythmias of the heart are typically associated with high-frequency rotating electric field waves or spirals. One standard method of terminating arrhythmias, often referred to as defibrillation, is applying a high intensity electric shock to the heart. The high voltage of up to several thousand volt and the resulting currents of some amperes, however, may cause serious damages to the heart and neighboring tissue. Further, defibrillation is painful for the patient which limits the acceptance of implanted defibrillators. Nevertheless, up to now, implanting such defibrillators are the method of choice with patients at risk for life-threatening arrhythmias.
Another established therapy of cardiac arrhythmias is anti-tachycardia pacing (ATP). In ATP the heart is paced faster than its intrinsic rate in the case of ventricular tachycardia. However, ATP fails to terminate high-frequency arrhythmias and fully developed ventricular fibrillation.
Patent application publication US 2006/0100670 A1, now U.S. Pat. No. 7,418,293, proposes cardiac stimulation methods and systems that provide for multiple pulse defibrillation. These methods and systems involve sensing a fibrillation event, determining a fibrillation cycle length associated with the fibrillation event, and delivering a plurality of defibrillation pulses to treat the fibrillation event. The defibrillation pulses are delivered using a combination of subcutaneous and non-intrathoracic electrodes. Delivery of each defibrillation waveform subsequent to a first defibrillation waveform is separated in time by a delay associated with the fibrillation cycle length. Particularly, delays between defibrillation waveform delivery are associated with a percentage of the fibrillation cycle length. The actual number of defibrillation pulses delivered in the embodiments of U.S. Pat. No. 7,418,293 is 2 or 3, particularly 2. The actual delay between the individual pulses is between about 50% and about 125% of the average cycle length and typically it is between about 75% and about 100% of the average cycle length, where the cardiac response to multiple separated pulses is similar to the cardiac response to a single pulse. This region, which is considered as similar to a region of constructive interference for the cardiac response to the separated response to the separated pulses, is told to provide opportunities for improved efficacy of defibrillation and/or decreased energy requirements for defibrillation systems.
A. Pumir et al.: “Wave Emission from Heterogeneities Opens a Way to Controlling Chaos in the Heart” (PRL 99, 208101 (2007)) suggest to use wave emission from heterogeneities (WEH) induced by periodic pulses of an electric field as a method of chaos control of waves in the heart. This method is said to be more effective than ATP and to require much less energy than the defibrillating shock. Particularly, the single pulses are of such a low electric field that they do not terminate a rotating wave, but the train of pulses applied in WEH can.
There is still a need for an easily workable regime of terminating a high frequency arrhythmic electric state of a heart with low electric field pulses causing as little tissue damage and pain as possible.